osrelease.sh

sys/conf/osrelease.sh underwent some editing back in November 2009 to
fix PR/42321, and in the process, its behavior with respect to
non-numeric version numbers changed... which I didn't notice until we
had one. :) 6.0_BETA is displayed as "6.0", which I think is not quite
what we want - but I'm not certain the most appropriate fix.